Dipeptidyl-peptidase IV from bench to bedside: an update on structural properties, functions, and clinical aspects of the enzyme DPP IV

Impact of dapagliflozin, an SGLT2 inhibitor, on serum levels of soluble dipeptidyl peptidase-4 in patients with type 2 diabetes and non-alcoholic fatty liver disease

AIMS

Soluble dipeptidyl peptidase-4 (sDPP-4) is secreted by hepatocytes and induces adipose tissue inflammation and insulin resistance. Sodium-glucose co-transporter-2 (SGLT2) inhibitors can improve hepatic steatosis by inhibiting hepatic de novo lipogenesis. We investigated the effects of dapagliflozin (an SGLT2 inhibitor) on serum levels of sDPP-4 in patients with type 2 diabetes and non-alcoholic fatty liver disease (NAFLD).

METHODS

Fifty-seven patients with type 2 diabetes and NAFLD were randomized to a dapagliflozin group (5 mg/d for 24 weeks) (n = 33) or the control group (n = 24). Serum levels of sDPP-4 were measured with a commercial ELISA kit. Visceral adipose tissue (VAT) and subcutaneous adipose tissue (SAT) areas were measured by dual bioelectrical impedance analysis.

RESULTS

In a total of 57 patients, baseline serum sDPP-4 was positively correlated with aspartate aminotransferase (AST), alanine aminotransferase (ALT), γ-glutamyl transferase (GGT) and HOMA-IR Both VAT and SAT areas decreased significantly in the dapagliflozin group alone. Liver enzymes were decreased at 24 weeks in the dapagliflozin group, but were unchanged in the control group. Although both groups showed significant reduction of serum sDPP-4 after 24 weeks of treatment, the magnitude of decrease was significantly larger in the dapagliflozin group. Changes in liver enzymes during treatment with dapagliflozin were positively correlated with the change in serum sDPP-4, but not with changes in VAT volume or HbA1c.

CONCLUSIONS

Improvement of liver dysfunction after treatment with dapagliflozin was associated with a decrease in serum sDPP-4, suggesting that reduction of serum sDPP-4 by SGLT2 inhibitors may be a therapeutic strategy for NAFLD/NASH in patients with type 2 diabetes that is independent of glucose lowering or weight loss.

Prediction of Bioactive Peptides from Chlorella sorokiniana Proteins Using Proteomic Techniques in Combination with Bioinformatics Analyses

Chlorella is one of the most nutritionally important microalgae with high protein content and can be a good source of potential bioactive peptides. In the current study, isolated proteins from Chlorella sorokiniana were subjected to in silico analysis to predict potential peptides with biological activities. Molecular characteristics of proteins were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and proteomics techniques. A total of eight proteins were identified by proteomics techniques from 10 protein bands of the SDS-PAGE. The predictive result by BIOPEP's profile of bioactive peptides tools suggested that proteins of C. sorokiniana have the highest number of dipeptidyl peptidase-IV (DPP IV) inhibitors, with high occurrence of other bioactive peptides such as angiotensin-I converting enzyme (ACE) inhibitor, glucose uptake stimulant, antioxidant, regulating, anti-amnestic and antithrombotic peptides. In silico analysis of enzymatic hydrolysis revealed that pepsin (pH > 2), bromelain and papain were proteases that can release relatively larger quantity of bioactive peptides. In addition, combinations of different enzymes in hydrolysis were observed to dispense higher numbers of bioactive peptides from proteins compared to using individual proteases. Results suggest the potential of protein isolated from C. sorokiniana could be a source of high value products with pharmaceutical and nutraceutical application potential.

Using DPP-4 inhibitors to modulate beta cell function in type 1 diabetes and in the treatment of diabetic kidney disease

INTRODUCTION

DPP-4 inhibitors have pleomorphic effects that extend beyond the anti-hyperglycemic labeled use of the drug. DPP-4 inhibitors have demonstrated promising renal protective effects in T2DM and T1DM and protective effects against immune destruction of pancreatic beta-cells in T1DM.

AREAS COVERED

The efficacy of DPP-4 inhibitors in the treatment of diabetic kidney disease and possible adjunct with insulin in the treatment of T1DM to preserve beta-cell function. Pertinent literature was identified through Medline, PubMed and ClinicalTrials.gov (1997-November 2018) using the search terms T1DM, sitagliptin, vildagliptin, linagliptin, beta-cell function, diabetic nephropathy. Only articles are written in the English language, and clinical trials evaluating human subjects were used.

EXPERT OPINION

DPP-4 inhibitors can be used safely in patients with diabetic kidney disease and do not appear to exacerbate existing diabetic nephropathy. Linagliptin reduces albuminuria and protects renal endothelium from the deleterious effects of hyperglycemia. The effects of DPP-4 inhibitors on preserving beta-cell function in certain subtypes of T1DM [e.g. Latent Autoimmune Diabetes in Adult (LADA) and Slowly Progressive Type 1 Diabetes (SPIDDM)] are encouraging and show promise.

Immunohistochemistry for Anti-diabetes Drug, Alogliptin Using a Newly Prepared Monoclonal Antibody: Its Precise Localization in Rat Small Intestine

Knowledge of time sequence of localization of drugs in cells and tissues of animals may help in developing a better understanding of the actual overall pharmacokinetics of the drugs. We produced monoclonal antibody (mAb) against alogliptin (AG), a dipeptidyl peptidase-4 (DPP-4) inhibitor, conjugated to BSA with N-(γ-maleimidobutyryloxy)-succinimide. The mAb was specific for AG and did not cross-react with sitagliptin, vancomycin or amoxicillin. The mAb enabled us to develop an immunohistochemical method for detecting the localization of AG in the rat small intestine. One hour after a single oral administration of AG, immunohistochemistry revealed that the immunoreactivity of AG was observed in almost all of cells and tissues of the duodenum. The microvilli of the absorptive epithelial cells were moderately stained. The staining pattern of AG at jejunum and ilium was almost the same as that of duodenum, but the staining intensity, especially at absorptive epithelial cells and intestinal gland epithelial cells, became stronger towards the distal part of the small intestine. These results suggested that AG may be more actively absorbed from the lower part of the small intestine than in the upper part. It may affect the function of cells with membrane-bound DPP-4 because it was reported that membrane-bound form of DPP-4 exists in the microvilli of the absorptive epithelial cells.

CD26/DPP4 - a potential biomarker and target for cancer therapy

CD26/dipeptidyl peptidase (DPP)4 is a membrane-bound protein found in many cell types of the body, and a soluble form is present in body fluids. There is longstanding evidence that various primary tumors and also metastases express CD26/DPP4 to a variable extent. By cleaving dipeptides from peptides with a proline or alanine in the penultimate position at the N-terminus, it regulates the activity of incretin hormones, chemokines and many other peptides. Due to these effects and interactions with other molecules, a tumor promoting or suppressing role can be attributed to CD26/DPP4. In this review, we discuss the existing evidence on the expression of soluble or membrane-bound CD26/DPP4 in malignant diseases, along with the most recent findings on CD26/DPP4 as a therapeutic target in specific malignancies. The expression and possible involvement of the related DPP8 and DPP9 in cancer are also reviewed. A higher expression of CD26/DPP4 is found in a wide variety of tumor entities, however more research on CD26/DPP4 in the tumor microenvironment is needed to fully explore its use as a tumor biomarker. Circulating soluble CD26/DPP4 has also been studied as a cancer biomarker, however, the observed decrease in most cancer patients does not seem to be cancer specific. Encouraging results from experimental work and a recently reported first phase clinical trial targeting CD26/DPP4 in mesothelioma, renal and urological tumors pave the way for follow-up clinical studies, also in other tumor entities, possibly leading to the development of more effective complementary therapies against cancer.

Soluble Dipeptidyl Peptidase-4 Levels Are Associated with Decreased Renal Function in Patients with Type 2 Diabetes Mellitus

BACKGROUND

Dipeptidyl peptidase-4 (DPP-4) is strongly expressed in the kidney, and soluble levels of this protein are used as a marker in various chronic inflammatory diseases, including diabetes, coronary artery disease, and cancer. This study examined the association between the serum soluble DPP-4 levels and renal function or cardiovascular risk in patients with type 2 diabetes mellitus.

METHODS

In this retrospective analysis, soluble DPP-4 levels were measured in preserved sera from 140 patients with type 2 diabetes mellitus who had participated in our previous coronary artery calcium (CAC) score study.

RESULTS

The mean±standard deviation soluble DPP-4 levels in our study sample were 645±152 ng/mL. Univariate analyses revealed significant correlations of soluble DPP-4 levels with the total cholesterol (r=0.214, P=0.019) and serum creatinine levels (r=-0.315, P<0.001) and the estimated glomerular filtration rate (eGFR; estimated using the modification of diet in renal disease equation) (r=0.303, P=0.001). The associations of soluble DPP-4 levels with serum creatinine and GFR remained significant after adjusting for age, body mass index, and duration of diabetes. However, no associations were observed between soluble DPP-4 levels and the body mass index, waist circumference, or CAC score.

CONCLUSION

These data suggest the potential use of serum soluble DPP-4 levels as a future biomarker of deteriorated renal function in patients with type 2 diabetes mellitus.

Polyalthia Clerodane Diterpene Potentiates Hypoglycemia via Inhibition of Dipeptidyl Peptidase 4

Serine protease dipeptidyl peptidase 4 (DPP-4) is involved in self/non-self-recognition and insulin sensitivity. DPP-4 inhibitors are conventional choices for diabetic treatment; however, side effects such as headache, bronchus infection, and nasopharyngitis might affect the daily lives of diabetic patients. Notably, natural compounds are believed to have a similar efficacy with lower adverse effects. This study aimed to validate the DPP-4 inhibitory activity of clerodane diterpene 16-hydroxycleroda-3,13-dien-15,16-olide (HCD) from Polyalthia longifolia, rutin, quercetin, and berberine, previously selected through molecular docking. The inhibitory potency of natural DPP-4 candidates was further determined by enzymatic, in vitro Caco-2, and ERK/PKA activation in myocyte and pancreatic cells. The hypoglycemic efficacy of the natural compounds was consecutively analyzed by single-dose and multiple-dose administration in diet-induced obese diabetic mice. All the natural-compounds could directly inhibit DPP-4 activity in enzymatic assay and Caco-2 inhibition assay, and HCD showed the highest inhibition of the compounds. HCD down-regulated LPS-induced ERK phosphorylation in myocyte but blocked GLP-1 induced PKA expression. For in vivo tests, HCD showed hypoglycemic efficacy only in single-dose administration. After 28-days administration, HCD exhibited hypolipidemic and hepatoprotective efficacy. These results revealed that HCD performed potential antidiabetic activity via inhibition of single-dose and long-term administrations, and could be a new prospective anti-diabetic drug candidate.

The proteome of frozen-thawed pig spermatozoa is dependent on the ejaculate fraction source

The preservation of sperm functional parameters and fertility post-cryopreservation largely varies in the porcine, a species with a fractionated ejaculate. Although intrinsic individual differences have primarily been linked to this variation, differences in protein abundance among frozen-thawed (FT)-spermatozoa are far more relevant. This study, performed in two experiments, looked for proteomic quantitative differences between FT-sperm samples differing in post-thaw viability, motility, apoptosis, membrane lipid peroxidation and nuclear DNA fragmentation. The spermatozoa were either derived from the sperm-rich ejaculate fraction (SRF) or the entire ejaculate (Experiment 1) or from the first 10 mL of the SRF, the remaining SRF and the post-SRF (Experiment 2). Quantitative sperm proteomic differences were analysed using a LC-ESI-MS/MS-based SWATH approach. In Experiment 1, FT-spermatozoa from the SRF showed better preservation parameters than those from the entire ejaculate, with 26 Sus scrofa proteins with functional sperm relevance showing relative quantitative differences (FC ≥ 1.5) between sperm sources. In Experiment 2, FT-spermatozoa from the first 10 mL of the SRF and the remaining SRF were qualitatively better than those from the post-SRF, and 187 proteins showed relative quantitative differences among the three ejaculate sources. The results indicate that quantitative proteome differences are linked to sperm cryosurvival.

From SARS to MERS, Thrusting Coronaviruses into the Spotlight

Coronaviruses (CoVs) have formerly been regarded as relatively harmless respiratory pathogens to humans. However, two outbreaks of severe respiratory tract infection, caused by the severe acute respiratory syndrome coronavirus (SARS-CoV) and the Middle East respiratory syndrome coronavirus (MERS-CoV), as a result of zoonotic CoVs crossing the species barrier, caused high pathogenicity and mortality rates in human populations. This brought CoVs global attention and highlighted the importance of controlling infectious pathogens at international borders. In this review, we focus on our current understanding of the epidemiology, pathogenesis, prevention, and treatment of SARS-CoV and MERS-CoV, as well as provides details on the pivotal structure and function of the spike proteins (S proteins) on the surface of each of these viruses. For building up more suitable animal models, we compare the current animal models recapitulating pathogenesis and summarize the potential role of host receptors contributing to diverse host affinity in various species. We outline the research still needed to fully elucidate the pathogenic mechanism of these viruses, to construct reproducible animal models, and ultimately develop countermeasures to conquer not only SARS-CoV and MERS-CoV, but also these emerging coronaviral diseases.

Glucagon-like peptide-1 (GLP-1) mediates the protective effects of dipeptidyl peptidase IV inhibition on pulmonary hypertension

Background

Pulmonary hypertension (PH) is a progressive disease leading to death ultimately. Our recently published data demonstrated that inhibiting dipeptidyl peptidase IV (DPP-4) alleviated pulmonary vascular remodeling in experimental PH. However, whether glucagon-like peptide-1 (GLP-1) mediated the protective effect of DPP-4 inhibition (DPP-4i) on PH is unclear.

Results

In the present study, GLP-1 receptor antagonist (exendin-3) abolished the protective effects of DPP-4 inhibitor (sitagliptin) on right ventricular systolic pressure (RVSP) and pulmonary vascular remodeling (PVR) in monocrotaline (MCT, 60 mg/kg)-induced PH in rat. Notably, activation of GLP-1 receptor by GLP-1 analogue liraglutide directly attenuated RVSP and PVR in MCT-induced PH, as well as bleomycin- and chronic hypoxia-induced PH. Moreover, liraglutide potently inhibited MCT-induced inflammation and suppressed MCT-induced down-regulation of vascular endothelial marker (VE-cadherin and vWF) in lung. In vitro studies showed liraglutide reversed TGF-β1 (5 ng/ml) combining IL-1β (5 ng/ml) induced endothelial-mesenchymal transition (EndMT) in human umbilical vein endothelial cells (HUVECs), which could be abolished by GLP-1 receptor antagonist (exendin-3). Furtermore, liraglutide suppressed TGF-β1-IL-1β-induced phosphorylation of both Smad3 and ERK1/2.

Conclusions

Our data suggest that GLP-1 mediated the protective effects of DPP-4i on pulmonary vascular and RV remodeling in experimental PH, which may be attributed to the inhibitory effect on EndMT.

Dipeptidyl Peptidase 4 Inhibition Ameliorates Chronic Kidney Disease in a Model of Salt-Dependent Hypertension

Cardiovascular diseases frequently coexist with chronic kidney disease that constitutes a major determinant of outcome in patients with heart failure. Dysfunction of both organs is related to chronic inflammation, endothelial dysfunction, oxidative stress, and fibrosis. Widespread expression of serine protease DPP4 that degrades varieties of substrates suggests its involvement in numerous physiological processes. In this study, we tested the effects of selective DPP4 inhibition on the progression of renal disease in a nondiabetic model of hypertensive heart disease using Dahl salt-sensitive rats. Chronic DPP4 inhibition positively affected renal function with a significant reduction in albuminuria and serum creatinine. DPP4 inhibition attenuated the inflammatory component by reducing the expression of NF-κB, TNFα, IL-1β, IL-6, and MCP-1. Kidney macrophages expressed GLP-1R, and DPP4 inhibition promoted macrophage polarization toward the anti-inflammatory M2 phenotype. Finally, high degrees of NADPH oxidase 4 expression and oxidation of nucleic acids, lipids, and proteins were reduced upon DPP4 inhibition. Our study provides evidence of renoprotection by DPP4 inhibition in a nondiabetic hypertension-induced model of chronic cardiorenal syndrome, indicating that DPP4 pathway remains a valid object to study in the context of chronic multiorgan diseases.

Identification of angiotensin converting enzyme and dipeptidyl peptidase-IV inhibitory peptides derived from oilseed proteins using two integrated bioinformatic approaches

Angiotensin-converting enzyme (ACE) and dipeptidyl peptidase-IV (DPP-IV) play critical roles in the development of hypertension and type 2 diabetes, respectively. Inhibiting ACE and DPP-IV activity using peptides has become part of new therapeutic strategies for supporting medicinal treatment of both diseases. In this study, oilseed proteins, including soybean, flaxseed, rapeseed, sunflower and sesame are evaluated for the possibility of generating ACE and DPP-IV inhibitory peptides using different integrated bioinformatic approaches (UniProt knowledgebase, ProtParam, BLAST, BIOPEP, PeptideRanker, Pepsite2 and ToxinPred), and three bovine proteins (β-lactoglobulin, β-casein and κ-casein) as comparisons. Compared with bovine proteins, the potency indices of ACE and DPP-IV inhibitory peptides, calculated using the BIOPEP database, suggest that oilseed proteins may be considered as good precursors of ACE inhibitory peptides but generate a relative lower yield of DPP-IV inhibitory peptides following subtilisin, pepsin (pH = 1.3) or pepsin (pH > 2) hydrolysis. Average scores aligned using PeptideRanker confirmed oilseed proteins as significant potential sources of bioactive peptides: over 105 peptides scored over 0.8. Pepsite2 predicted that these peptides would largely bind via Gln281, His353, Lys511, His513, Tyr520 and Tyr523 of ACE to inhibit the enzyme, while Trp629 would be the predominant binding site of peptides in reducing DPP-IV activity. All peptides were capable of inhibiting ACE and DPP-IV whilst 65 of these 105 peptides are not currently recorded in BIOPEP database. In conclusion, our in silico study demonstrates that oilseed proteins could be considered as good precursors of ACE and DPP-IV inhibitory peptides as well as so far unexplored peptides that potentially have roles in ACE and DPP-IV inhibition and beyond.

Dipeptidyl Peptidase 4 Activity Is Related to Body Composition, Measures of Adiposity, and Insulin Resistance in Subjects with Excessive Adiposity and Different Degrees of Glucose Tolerance

BACKGROUND

The enzyme dipeptidyl peptidase 4 (DPP4) has been recently recognized as an adipo-myokine. However, studies that associate its constitutive activity with body composition, anthropometry, and insulin resistance (IR) are very scarce and included only healthy people.

METHODS

First, we investigated the relationships of constitutive DPP4 activity, body composition (assessed by bioelectrical impedance analysis), and measures of adiposity and IR in fifty-two subjects of both sexes, 18-50 years, and BMI ≥25.0 kg/m² who comprised three groups according to glucose tolerance. Additionally, we evaluated associations among DPP4 activity and adipokines, gut peptides, and biochemical variables at fasting and 30 and 60 min after a standardized meal intake.

RESULTS

DPP4 activity was no different among the three groups. At fasting, pooled analysis showed it was positively correlated with measures of central adiposity, such as WC (P = 0.011) and WHR (P = 0.009), and with all measures of IR, but inversely related to indexes of general adiposity, such as fat mass percentage (P = 0.014) and BAI (P = 0.0003). DPP4 activity was also associated with lean mass (r = 0.57, P < 0.0001). After meal intake, DPP4 activity remained significantly associated with insulin, leptin, and resistin. In multiple regression analysis, BAI, WHR, percent lean mass, HOMA-IR, and leptin influenced DPP4 activity and explained approximately 26% of the variance on it.

CONCLUSIONS

Constitutive DPP4 activity is positively associated with lean mass, central adiposity, and IR and negatively to general adiposity. Furthermore, it seems to be influenced by body composition and IR and could also be viewed as an adipo-myokine in subjects with excessive adiposity and different stages of glucose tolerance.

Physiology and Pharmacology of DPP-4 in Glucose Homeostasis and the Treatment of Type 2 Diabetes

Dipeptidyl peptidase-4 (DPP-4), also known as the T-cell antigen CD26, is a multi-functional protein which, besides its catalytic activity, also functions as a binding protein and a ligand for a variety of extracellular molecules. It is an integral membrane protein expressed on cells throughout the body, but is also shed from the membrane and circulates as a soluble protein in the plasma. A large number of bioactive molecules can be cleaved by DPP-4 in vitro, but only a few of these have been demonstrated to be physiological substrates. One of these is the incretin hormone, glucagon-like peptide-1 (GLP-1), which plays an important role in the maintenance of normal glucose homeostasis, and DPP-4 has been shown to be the key enzyme regulating its biological activity. This pathway has been targeted pharmacologically through the development of DPP-4 inhibitors, and these are now a successful class of anti-hyperglycaemic agents used to treat type 2 diabetes (T2DM). DPP-4 may additionally influence metabolic control via its proteolytic effect on other regulatory peptides, but it has also been reported to affect insulin sensitivity, potentially mediated through its non-enzymatic interactions with other membrane proteins. Given that altered expression and activity of DPP-4 are associated with increasing body mass index and hyperglycaemia, DPP-4 has been proposed to play a role in linking obesity and the pathogenesis of T2DM by functioning as a local mediator of inflammation and insulin resistance in adipose and hepatic tissue. As well as these broader systemic effects, it has also been suggested that DPP-4 may be able to modulate β-cell function as part of a paracrine system involving GLP-1 produced locally within the pancreatic islets. However, while it is evident that DPP-4 has the potential to influence glycaemic control, its overall significance for the normal physiological regulation of glucose homeostasis in humans and its role in the pathogenesis of metabolic disease remain to be established.

Role of dipeptidyl peptidase-4 as a potentiator of activin/nodal signaling pathway

DPP4 (dipeptidyl peptidase-4), a highly conserved transmembrane glycoprotein with an exo-peptidase activity, has been shown to contribute to glucose metabolism, immune regulation, signal transduction, and cell differentiation. Here, we show that DPP4 is involved in control of activin/nodal signaling in Xenopus early development. In support of this, gain of function of DPP4 augmented Smad2 phosphorylation as well as expression of target genes induced by activin or nodal signal. In addition, Dpp4 and Xnr1 showed synergistic effect on induction of ectopic dorsal body axis, when co-injected at suboptimal doses in early embryos. Conversely, saxagliptin, a DPP4 inhibitor repressed activin induction of Smad2 phosphorylation. Notably, overexpression of Dpp4 disrupted specification of dorsal body axis of embryo, leading to malformed phenotypes such as spina bifida and a shortened and dorsally bent axis. Together, these results suggest that DPP4 functions as a potentiator of activin/nodal signaling pathway.

Analysis of the Correlation between the Myocardial Expression of DPP-4 and the Clinical Parameters of Patients with Heart Failure

Dipeptidyl peptidase-4 (DPP-4) inhibitors are widely used as antidiabetic drugs. We recently reported that DPP-4 inhibition has beneficial effects on heart failure (HF) mice model. Furthermore, we confirmed that myocardial DPP-4 activity was significantly increased in HF mice compared with non-HF mice. The aim of this study was to investigate the level of myocardial CD26 (DPP-4) expression and its association to clinical parameters in HF patients.Endomyocardial biopsy (EMB) specimens (n = 33) were obtained from HF patients who were admitted to Chiba University Hospital from June 2006 to July 2012. EMB specimens were fixed in formaldehyde and stained with Masson's trichrome staining or with anti-CD26 antibody. Patients were divided into the high CD26 density (CD26-H) or low CD26 density groups (CD26-L). DPP-4 density was compared with blood brain natriuretic peptide (BNP) level and echocardiographic parameters at one year after EMB. Although there were no significant differences in echocardiographic parameters between the CD26-H group and CD26-L group, blood BNP levels were higher in the CD26-H group than in the CD26-L group at one year after EMB. Multivariate regression analysis showed that CD26 density was also an independent determinant of blood BNP levels at one year after EMB.The level of myocardial CD26 expression might be a predictive marker of prognosis in patients with HF.

Lysosomal Proteases Are a Determinant of Coronavirus Tropism

Cell entry by coronaviruses involves two principal steps, receptor binding and membrane fusion; the latter requires activation by host proteases, particularly lysosomal proteases. Despite the importance of lysosomal proteases in both coronavirus entry and cell metabolism, the correlation between lysosomal proteases and cell tropism of coronaviruses has not been established. Here, we examined the roles of lysosomal proteases in activating coronavirus surface spike proteins for membrane fusion, using the spike proteins from severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV) as the model system. To this end, we controlled the contributions from receptor binding and other host proteases, thereby attributing coronavirus entry solely or mainly to the efficiency of lysosomal proteases in activating coronavirus spike-mediated membrane fusion. Our results showed that lysosomal proteases from bat cells support coronavirus spike-mediated pseudovirus entry and cell-cell fusion more effectively than their counterparts from human cells. Moreover, purified lysosomal extracts from bat cells cleave cell surface-expressed coronavirus spikes more efficiently than their counterparts from human cells. Overall, our study suggests that different lysosomal protease activities from different host species and tissue cells are an important determinant of the species and tissue tropism of coronaviruses.IMPORTANCE Coronaviruses are capable of colonizing new species, as evidenced by the recent emergence of SARS and MERS coronaviruses; they can also infect multiple tissues in the same species. Lysosomal proteases play critical roles in coronavirus entry by cleaving coronavirus surface spike proteins and activating the fusion of host and viral membranes; they also play critical roles in cell physiology by processing cellular products. How do different lysosomal protease activities from different cells impact coronavirus entry? Here, we controlled the contributions from known factors that function in coronavirus entry so that lysosomal protease activities became the only or the main determinant of coronavirus entry. Using pseudovirus entry, cell-cell fusion, and biochemical assays, we showed that lysosomal proteases from bat cells activate coronavirus spike-mediated membrane fusion more efficiently than their counterparts from human cells. Our study provides the first direct evidence supporting lysosomal proteases as a determinant of the species and tissue tropisms of coronaviruses.

A Multi-Mode Bioactive Agent Isolated From Ficus microcarpa L. Fill. With Therapeutic Potential for Type 2 Diabetes Mellitus

Type 2 diabetes is a metabolic disorder, characterized by hyperglycemia and glucose intolerance. Natural products and its derived active compounds may be achievable alternatives for the treatment of type 2 diabetes. In present study we investigated the antidiabetic potential of Ficus microcarpa and isolated bioactive compounds i.e., Plectranthoic acid A (PA-A) and 3,4,5,7-Flavantetrol (FL). Anti-hyperglycemic potential was evaluated via α-glucosidase, α-amylase and dipeptidyl peptidase 4 (DPP-4) assays. 5'AMP-activated kinase (AMPK) activation potential was assessed by using primary hepatocytes. Distribution of PA-A in different parts of Ficus microcarpa was evaluated by using rapid high-performance liquid chromatography (HPLC). Ethyl acetate fraction (FME) exhibited significant inhibition of α-glucosidase, α-amylase, and DPP-4, therefore, was selected for isolation of bioactive compounds. Among isolated compounds PA-A was more potent and possessed pleotropic inhibitory activity with IC50 values of 39.5, 55.5, and 51.4 μM against α-glucosidase, α-amylase, and DPP-4, respectively. Our results showed that PA-A is also a potent activator of AMPK which is a central hub of metabolic regulation. Molecular docking studies confirmed the activity of PA-A against α-glucosidase, α-amylase, and DPP-4. Rapid HPLC method revealed that maximum concentration of PA-A is present in the stem (2.25 μg/mg dry weight) of Ficus microcarpa. Both in vitro and in silico studies proposed that Ficus microcarpa and its isolated compound PA-A could be an important natural source for alleviating the symptoms of type 2 diabetes mellitus and we suggest that PA-A should be explored further for its ultimate use for the treatment of type 2 diabetes.

DPP4 inhibition by sitagliptin attenuates LPS-induced lung injury in mice

Acute respiratory distress syndrome (ARDS) is a severe clinical condition marked by acute respiratory failure and dysregulated inflammation. Pulmonary vascular endothelial cells (PVECs) function as an important pro-inflammatory source in ARDS, suggesting that modulation of inflammatory events at the endothelial level may have a therapeutic benefit. Dipeptidyl peptidase-4 (DPP4) inhibitors, widely used for the treatment of diabetes mellitus, have been reported to have possible anti-inflammatory effects. However, the potential anti-inflammatory effects of DPP4 inhibition on PVEC function and ARDS pathophysiology are unknown. Therefore, we evaluated the effects of sitagliptin, a DPP4 inhibitor in wide clinical use, on LPS-induced lung injury in mice and in human lung ECs in vitro. In vivo, sitagliptin reduced serum DPP4 activity, bronchoalveolar lavage protein concentration, cell number, and proinflammatory cytokine levels after LPS and alleviated histological findings of lung injury. LPS decreased the expression levels of CD26/DPP4 on pulmonary epithelial cells and PVECs isolated from mouse lungs, and the effect was partially reversed by sitagliptin. In vitro, human lung microvascular ECs (HLMVECs) expressed higher levels of CD26/DPP4 than human pulmonary arterial ECs. LPS induced the release of TNFα, IL-6, and IL-8 by HLMVECs that were inhibited by sitagliptin. LPS promoted the proliferation of HLMVECs, and sitagliptin suppressed this response. However, sitagliptin failed to reverse LPS-induced permeability in cultured ECs or lung epithelial cells in vitro. In summary, sitagliptin attenuates LPS-induced lung injury in mice and exerts anti-inflammatory effects on HLMVECs. These novel observations indicate DPP4 inhibitors may have potential as therapeutic drugs for ARDS.

Sodium acetate improves disrupted glucoregulation and hepatic triglyceride content in insulin-resistant female rats: involvement of adenosine deaminase and dipeptidyl peptidase-4 activities

Combined oral contraceptive (COC) treatment has been shown to be associated with glucose deregulation and increased triglyceride levels, but the mechanisms are elusive. Soluble dipeptidyl peptidase-4 (sDPP-4) and adenosine deaminase (ADA) are involved in the initiation and/or progression of cardiometabolic disorders. We therefore, hypothesized that increased DPP-4 and ADA activities are involved in glucose deregulation and hepatic triglyceride accumulation induced by COC treatment. This study also investigated whether short-chain fatty acid, acetate, would protect against COC-induced dysmetabolic effects. Female Wistar rats received (p.o.) vehicle and COC (1.0 μg ethinylestradiol plus 5.0 μg levonorgestrel) with or without sodium acetate (ACE; 200 mg) for 8 weeks. Treatment with COC led to increased plasma triglyceride-glucose index, 1-h postload glucose response, insulin, free fatty acid, insulin resistance, and impaired glucose tolerance. COC treatment also resulted in increased plasma and hepatic triglycerides (TG), TG/HDL-cholesterol ratio, malondialdehyde, uric acid, lactate dehydrogenase, DPP-4, ADA, and xanthine oxidase (XO) activities. On the other hand, COC led to reduction in nitric oxide level. However, ACE significantly ameliorated the alterations induced by COC treatment, but XO activity remains elevated during COC treatment. This result also demonstrates that increased DPP-4 and ADA activities are at least in part involved in glucose deregulation and hepatic TG accumulation induced by COC treatment. Therefore, sodium acetate would impact positively on cardiometabolic disorders, at least in part, by inhibition of DPP-4 and ADA activities.

Dipeptidyl peptidase IV (DPP-4) inhibition alleviates pulmonary arterial remodeling in experimental pulmonary hypertension

Dipeptidyl peptidase IV (DPP-4) is well known for its role in glucose homeostasis, and DPP-4 inhibitor (DPP-4i) exhibits multiple actions in cardiovascular diseases. However, the effect of DPP-4i on pulmonary hypertension (PH) remains unclear. Therefore, this study aims to investigate the effect of DPP-4i on pulmonary arterial remodeling in rats with PH and the potential underlying mechanisms. Our results show that DPP-4 was expressed in epithelial cells, endothelial cells, smooth muscle cells, and inflammatory cells in lung. DPP-4i (Sitagliptin) attenuated right ventricular systolic pressure (RVSP), right ventricle remodeling, hypertrophy of pulmonary arterial medial layer, inflammatory cell infiltration, and endothelial-mesenchymal transition (EndMT) in monocrotaline (MCT)-induced PH rats. Similarly, DPP-4i also alleviated bleomycin- and chronic hypoxia-induced PH in rats. In cultured human pulmonary arterial smooth muscle cells (PASMCs), DPP-4i inhibited platelet derived growth factor (PDGF)-BB-induced proliferation and migration, which was abolished by phosphatase and tensin homolog deleted on chromosome ten (PTEN) knockout. These results demonstrate that DPP-4 inhibition alleviates pulmonary arterial remodeling in experimental PH by inhibiting proliferation and migration of PASMCs.

Periostin and Dipeptidyl Peptidase-4: Potential Biomarkers of Interleukin 13 Pathway Activation in Asthma and Allergy

Periostin and dipeptidyl peptidase-4 (DPP-4) are proteins induced by type 2 cytokines interleukin (IL)-4 and IL-13 and show increased expression in asthma and diseases with type 2 inflammation, including atopic dermatitis and chronic rhinosinusitis. Both proteins can also be induced by other stimuli, such as profibrotic factors, which may confound their specificity as biomarkers of IL-13 pathway activation and type 2-driven disease. DPP-4 is important in glucose metabolism; therefore, serum concentrations may be confounded by the presence of concomitant metabolic disease. This review evaluates the potential of these biomarkers for anti-IL-13-directed therapy in asthma and diseases with type 2 inflammation.

Dipeptidyl Peptidase 4 Inhibitors Reduce Hepatocellular Carcinoma by Activating Lymphocyte Chemotaxis in Mice

BACKGROUND & AIMS

CD26, a multifunctional transmembrane glycoprotein, is expressed in various cancers and functions as dipeptidyl peptidase 4 (DPP4). We investigated whether CD26 expression is associated with hepatocellular carcinoma (HCC) progression and whether DPP4 inhibitors exert antitumor effects against HCC.

METHODS

CD26 expression was examined in 41 surgically resected HCC specimens. The effects of DPP4 inhibitors on HCC were examined by using HCC cell lines (Huh-7 and Li-7), xenograft tumors in nude mice, and a nonalcoholic steatohepatitis-related HCC mouse model.

RESULTS

CD26 expression in HCC specimens was associated with increased serum DPP4 activity, as well as a more advanced stage, less tumor immunity, and poorer prognosis in HCC patients. The HCC cell lines and xenograft tumors exhibited CD26 expression and DPP4 activity. The DPP4 inhibitors did not exhibit antitumor effects in vitro, but natural killer (NK) and/or T-cell tumor accumulation suppressed growth of xenograft tumor and HCC in vivo. The antitumor effects of DPP4 inhibitors were abolished by the depletion of NK cells or the neutralization of CXCR3, a chemokine receptor on NK cells. EZ-TAXIScan, an optical horizontal chemotaxis apparatus, identified enhanced NK and T-cell chemotaxis by DPP4 inhibitors ex vivo in the presence of Huh-7 cells and the chemokine CXCL10, which binds to CXCR3. The DPP4 inhibitors prevented the biologically active form of CXCL10 from being truncated by Huh-7 cell DPP4 activity. DPP4 inhibitors also suppressed tumor angiogenesis.

CONCLUSIONS

These results provide a rationale for verifying whether DPP4 inhibitors clinically inhibit the progression of HCC or augment the antitumor effects of molecular-targeting drugs or immunotherapies against HCC.

A manganese-salen complex as dipeptidyl peptidase IV inhibitor for the treatment of type 2 diabetes

A manganese Schiff base complex with N,N'-1,2-phenylenediamine-bis(salicyladimine) was synthesized and characterized by X-ray crystallography. This complex was administered intragastrically to alloxan-diabetic mice 3 weeks. In vivo tests showed that the complex significantly lowered serum glucose levels in alloxan-diabetic mice at doses of 77 mg V kg^-1. Meanwhile, this complex was investigated as dipeptidyl peptidase IV (DPP-IV) inhibitor for the treatment of type 2 diabetes. The compound exhibit moderate inhibition against DPP-IV and possessed an IC₅₀ value of 30 μM. Lineweaver-Burk transformation of the inhibition kinetics data demonstrated that it was a noncompetitive inhibitor of DPP-IV and Ki value was 136.3 μM. Moreover, molecular modeling studies suggested that the complex could fit well within the active-site cleft of DPP-IV. An acute toxicity study showed that animals treated intragastically with complex 1 at a dose of 5.0 g/kg did not show any significantly abnormal signs. These preliminary results suggest that the manganese Schiff base complex can induce a hypoglycemic effect in alloxan-diabetic mice.

A Human DPP4-Knockin Mouse's Susceptibility to Infection by Authentic and Pseudotyped MERS-CoV

Infection by the Middle East respiratory syndrome coronavirus (MERS-CoV) causes respiratory illness and has a high mortality rate (~35%). The requirement for the virus to be manipulated in a biosafety level three (BSL-3) facility has impeded development of urgently-needed antiviral agents. Here, we established anovel mouse model by inserting human dipeptidyl peptidase 4 (hDPP4) into the Rosa26 locus using CRISPR/Cas9, resulting in global expression of the transgene in a genetically stable mouse line. The mice were highly susceptible to infection by MERS-CoV clinical strain hCoV-EMC, which induced severe diffuse pulmonary disease in the animals, and could also be infected by an optimized pseudotyped MERS-CoV. Administration of the neutralizing monoclonal antibodies, H111-1 and m336, as well as a fusion inhibitor peptide, HR2P-M2, protected mice from challenge with authentic and pseudotyped MERS-CoV. These results confirmed that the hDPP4-knockin mouse is a novel model for studies of MERS-CoV pathogenesis and anti-MERS-CoV antiviral agents in BSL-3 and BSL-2facilities, respectively.

Soybean- and Lupin-Derived Peptides Inhibit DPP-IV Activity on In Situ Human Intestinal Caco-2 Cells and Ex Vivo Human Serum

Recent investigations have focused on food-derived peptides as novel natural inhibitors of dipeptidyl peptidase IV (DPP-IV), a new target for diabetes. This study aimed to optimize fast, sensitive, and cost-effective DPP-IV assays in situ on human intestinal Caco-2 cells and ex vivo on human serum. Both assays were applied to investigate the inhibitory activity of soy and lupin peptides. The best conditions for in situ DPP-IV activity in Caco-2 cells were obtained using 2-day cells and 50 µM Gly-Pro-AMC. Sitagliptin, used as reference inhibitor, showed a dose-dependent response with a 50% inhibition concentration (IC₅₀) of 0.6 µM. A lower IC₅₀ (0.2 µM) was obtained for sitagliptin on human serum incubated with the substrate for 24 h. Both assays were applied to assess the activity of Lup1 (LTFPGSAED) and Soy1 (IAVPTGVA) on DPP-IV. Lup1 and Soy1 inhibited DPP-IV in situ, with IC₅₀ values of of 207.5 and 223.2 µM, respectively, and maintained their inhibitory activity ex vivo on circulating DPP-IV with a slightly lower potency. These assays can be used to characterize the DPP-IV inhibitory activity of food-derived molecules more accurately than in vitro biochemical tests. This combined approach also considers their effects on the circulating form of DPP-IV, correlated to metabolic diseases.

Is glucagon-like peptide-1 fully protected by the dipeptidyl peptidase 4 inhibitor sitagliptin when administered to patients with type 2 diabetes?

AIM

To evaluate the relationship between plasma dipeptidyl-peptidase 4 (DPP-4) activity and its protection of glucagon-like peptide-1 (GLP-1) using the DPP-4 inhibitor sitagliptin.

METHODS

On four separate days, patients with type 2 diabetes (T2D) (n = 8; age: 59.9 ±10.8 [mean ±SD] years; body mass index [BMI]: 28.8 ±4.6 kg/m² ; glycated haemoglobin A1c [HbA1c]: 43.1 ±0.5 mmol/mol [6.6% ±1.7%]) received a 380-minute continuous intravenous infusion of GLP-1 (1.0 pmol × kg bodyweight^-1  × minutes^-1 ) and a double-blind, single-dose oral administration of sitagliptin in doses of 0 (placebo), 25, 100 and 200 mg.

RESULTS

Plasma DPP-4 activity decreased compared to baseline (placebo) with increasing doses of sitagliptin (P < .01), reaching a maximal inhibition with the 100 mg dose. Levels of intact GLP-1 increased with increasing doses of sitagliptin from placebo to 100 mg (area under curve [AUC] 7.2 [95%, CI; 12.1, 16.4] [placebo], 10.7 [16.1, 21.4] [25 mg], 11.7 [17.8, 23.6] [100 mg] nmol/L × 360 minutes [P < .01]), but no further increase in intact GLP-1 levels was observed with 200 mg of sitagliptin (11.5 [17.6, 23.4] nmol/L × 360 minutes) (P = .80).

CONCLUSION

Our findings suggest that the sitagliptin dose of 100 mg is sufficient to inhibit both plasma and membrane-bound DPP-4 activity, presumably also leading to complete protection of endogenous GLP-1 in patients with T2D.

High DPP-4 Concentrations in Adolescents Are Associated With Low Intact GLP-1

CONTEXT

Dipeptidyl peptidase 4 (DPP-4) metabolizes glucagon-like peptide-1 (GLP-1), and increased DPP4 levels are associated with obesity and visceral adiposity in adults.

OBJECTIVE

Investigating DPP-4 levels in adolescents and their association with (1) circulating intact GLP-1 levels and glucose tolerance; (2) body mass index (BMI); and (3) visceral, subcutaneous, and liver fat compartments.

DESIGN

Cross-sectional study, July 2012 to April 2015.

SETTING

Pediatric obesity clinic, Uppsala University Hospital.

PATIENTS AND PARTICIPANTS

Children and adolescents with obesity (n = 59) and lean controls (n = 21) aged 8 to 18 years.

MAIN OUTCOME MEASURES

BMI SD score, fasting plasma concentrations of DPP-4, total and intact GLP-1, fasting and oral glucose tolerance test (OGTT) concentrations of glucose, and visceral adipose tissue (VAT) and subcutaneous adipose tissue volumes and liver fat fraction.

RESULTS

Plasma DPP-4 levels decreased with age in both obese (41 ng/mL per year) and lean subjects (48 ng/mL per year). Plasma DPP-4 levels were higher in males in both the obesity and lean groups. With adjustments for age and sex, plasma DPP-4 level was negatively associated with intact GLP-1 at fasting (β = -12.3; 95% CI: -22.9, -1.8) and during OGTT (β = -12.1; 95% CI: -22.5, -1.7). No associations were found between DPP-4 and plasma glucose levels measured at fasting or after a 2-hour OGTT. Plasma DPP-4 level was 19% higher in obese subjects. Among adipose tissue compartments, the strongest association was with VAT (β = 0.05; 95% CI: -0.02, 0.12).

CONCLUSIONS

In adolescents, high plasma DPP-4 concentrations were associated with low proportions of intact GLP-1, high BMI, young age, and male sex. The observed associations are compatible with increased metabolism of GLP-1 in childhood obesity.

Constitutive DPP4 activity, inflammation, and microvascular reactivity in subjects with excess body weight and without diabetes

OBJECTIVE

In patients with diabetes, dipeptidyl peptidase 4 (DPP4) inhibition is associated with attenuation of inflammation and endothelial dysfunction. Here, we investigated the associations between constitutive DPP4 activity, inflammatory biomarkers, and microvascular reactivity in subjects with excess body weight without diabetes.

METHODS

Forty subjects of BMI ≥ 25.0 kg/m² and without diabetes were cross-sectionally evaluated. We assessed microvascular blood flow and vasomotion by laser Doppler flowmetry, and measured at baseline, 30, and 60 min after a standardized meal: DPP4 activity, glucose, insulin, hs-CRP, TNF-α, IL-6, PAI-1, ICAM-1, and VCAM-1. HOMA-IR and HOMA-AD were used to assess insulin resistance. Linear correlations of DPP4 activity with the biomarkers of inflammation and components of microvascular function were conducted. In step further, multiple regression analyses were performed to test whether some of these variables could influence, or be influenced by, the plasma DPP4 activity.

RESULTS

DPP4 activity was inversely associated with VCAM-1 at baseline (P < 0.05), and DPP4 activity_AUC was inversely correlated with the myogenic component_AUC of vasomotion (P < 0.05). In multiple regression analysis, HOMA-AD, IL-6, VCAM-1, PAI-1, blood flow, and vasomotion influenced DPP4 activity and explained almost 40% of the variance on it. When HOMA-AD, VCAM-1, and blood flow were placed respectively as dependent variables, DPP4 activity exerted a significant effect in all of them.

CONCLUSIONS

Constitutive DPP4 activity was associated with early markers of endothelial proinflammatory activation and microvascular function, and may have an influence and even be influenced by inflammation and microvascular blood flow in subjects with excess body weight without diabetes.

Gestational glucocorticoid exposure disrupts glucose homeostasis that is accompanied by increased endoglin and DPP-4 activity instead of GSK-3 in rats

Gestational glucocorticoid (GC) treatment has been associated with cardiometabolic disorder (CMD) in offspring's in later life. Elevated dipeptidyl peptidase-4 (DPP-4) activity, endoglin and glycogen synthase kinase-3 (GSK-3) has also been implicated in the development of insulin resistance (IR) and/or vascular inflammation. We aimed to investigate the impact of GC exposure on glucose metabolism and the circulating levels of inflammatory biomarkers, DPP-4 activity and GSK-3 in pregnant rats. Pregnant Wistar rats received either vehicle or dexamethasone (DEX; 0.2 mg/kg; po) between gestational days 14 and 19. Gestational GC exposure resulted in impaired glucose homeostasis that is accompanied with elevated circulating levels of inflammatory biomarkers (endoglin, uric acid, and platelet/lymphocyte ratio), oxidative stress (malondialdehyde), blood viscosity, reduced NO level and increased DPP-4 activity. However, these effects were associated with atherogenic dyslipidemia and reduced GSK-3.We conclude that plasma endoglin, a marker of vascular inflammation, and plasma DPP-4 activity are increased in pregnant rats treated with GC during late gestation. Therefore, glucose deregulation associated with gestational GC exposure is through endoglin-/DPP-4-dependent but GSK-3-independent pathway.

Plant dipeptidyl peptidase-IV inhibitors as antidiabetic agents: a brief review

Diabetes mellitus is an increasing public health problem in the world. Type 2 diabetes is the most common type of diabetes whose complications contribute to its high death rate. It seriously impacts healthcare systems and patients' quality of life. Therefore, effective measures and new treatment strategies are needed to solve this increasingly serious global problem. In recent years, inhibition of dipeptidyl peptidase IV (DPP-IV) has emerged as a new treatment option for Type 2 diabetes. This article reviews various plant DPP-IV inhibitors that showed inhibition toward enzyme as a major target for the management of Type 2 diabetes. These studies can contribute to the future development of DPP-IV inhibitors as drugs.

DPP-4 inhibitors and heart failure: a potential role for pharmacogenomics

There remains an ongoing controversy regarding the safety of dipeptidyl peptidase-4 (DPP-4) inhibitors and the risk of developing heart failure (HF). In addition, none of the animal studies suggested a mechanism for the DPP-4 inhibitors and HF risk. To date, advances in pharmacogenomics have enabled the identification of genetic variants in DPP-4 gene. Studies have shown that genetic polymorphisms in the gene encoding DPP-4 may be associated with potential pathways involved in HF risk. This review discusses the contradictory findings of DPP-4 inhibitors and HF and a potential role for pharmacogenomics. Pharmacogenomics of DPP-4 inhibitors is promising, and genetic information from randomized control trials is urgently needed to gain a full understanding of the safety of DPP-4 inhibitors and the risk of HF.

The effect of CD26-deficiency on dipeptidyl peptidase 8 and 9 expression profiles in a mouse model of Crohn's disease

The involvement of dipeptidyl peptidase (DP) IV/CD26 (DPP IV/CD26) family members in the pathogenesis of Crohn's disease (CD), an autoimmune inflammatory condition of the gut, is effected mainly through proteolytic cleavage of immunomodulatory substrates and DPP IV/CD26's costimulatory function. DP8 and DP9 are proteases with diverse functions including cell interactions, apoptosis, and immune response but their localization remains to be clarified. We assessed the impact of DPP IV/CD26 deficiency (CD26^-/- ) on the expression profiles of DP8 and DP9 by qPCR and immunodetection as well as quantified DP8/9 enzyme activity in distinctive phases of a chemically-induced CD model in mice. CD26^-/- did not affect colon DP8 mRNA expression, while the physiological concentration of DP8 protein is decreased in CD26^-/- mice but rises in inflammation (P < 0.05). On the other hand, DP9 mRNA level is significantly increased in CD26^-/- mice in inflammation as well as healing with the DP9 concentration being almost twofold increased (P < 0.05) in all experimental points in CD26^-/- mice compared to wild-type indicating the expected up-regulation in CD26^-/- conditions. Surprisingly, dominantly intracellular DP8 and DP9 were found in abundance in serum. DP8/9 activity is decreased in the inflamed colon, whereas its contribution to the overall serum DPP IV/CD26-like activity is negligible, suggesting the importance of their extra-enzymatic functions. To summarize, CD induction generated gene, protein and enzymatic changes of DP8 and DP9 so their involvement in inflammation development and/or healing process is implicated, especially in CD26^-/- , and the question of their subcellular localization should be revised.

Effect of enzymatic hydrolysis on bioactive properties and allergenicity of cricket (Gryllodes sigillatus) protein

Food-derived bioactive peptides have gained attention for their role in preventing chronic diseases. Edible insects are viable sources of bioactive peptides owing to their high protein content and sustainable production. In this study, whole crickets (Gryllodes sigillatus) were alcalase-hydrolyzed to a degree of hydrolysis (DH) ranging from 15 to 85%. Antioxidant activity, angiotensin converting enzyme (ACE), and dipeptidyl peptidase-4 (DPP-IV)- inhibition of the cricket protein hydrolysates (CPH) were evaluated before and after simulated gastrointestinal digestion (SGD). Antioxidant activity was similar among CPH, whereas ACE and DPP-IV inhibition was greater (p < 0.05) in CPH with 60-85% DH. Bioactivity improved after SGD. CPH allergenicity was evaluated using human shrimp-allergic sera. All sera positively reacted to tropomyosin in the unhydrolyzed cricket and CPH with 15-50% DH, whereas 60-85% DH showed no reactivity. In conclusion, CPH (60-85% DH) had the greatest bioactive potential and lowest reactivity to tropomyosin, compared with other CPH and the unhydrolyzed control.

Dipeptidyl peptidase-4 inhibition and renoprotection: the role of antifibrotic effects

PURPOSE OF REVIEW

This article analyzes the potential beneficial effects of dipeptidyl peptidase (DPP)-4 inhibitors on renal diseases.

RECENT FINDINGS

The pathological significance of DPP-4, either dependent or independent on catalytic activities, on renal diseases has been reported in preclinical studies. With regard to this, we have shown that damaged endothelial cells are converted to a mesenchymal cell phenotype, which is associated with the induction of DPP-4 in endothelial cells. The endothelial mesenchymal transition may contribute to kidney fibrosis; indeed, the antifibrotic effects of DPP-4 inhibitors have been reported elsewhere. However, even though such potential benefits of DPP-4 inhibitors on renal diseases were shown in preclinical studies, clinical trials have not yet revealed significant benefits in renal hard outcomes of DPP-4 inhibitors.

SUMMARY

To completely understand the beneficial effects of DPP-4 inhibitors, both the following studies are required: first, preclinical studies that analyze deeper molecular mechanisms of DPP-4 inhibition, and, second, clinical studies that investigate whether such potential beneficial effects of DPP-4 inhibitors are relevant to the patients in the clinic.

Reduction of soluble dipeptidyl peptidase 4 levels in plasma of patients infected with Middle East respiratory syndrome coronavirus

Dipeptidyl peptidase 4 (DPP4) is a receptor for MERS-CoV. The soluble form of DPP4 (sDPP4) circulates systematically and can competitively inhibit MERS-CoV entry into host cells. Here, we measured the concentration of sDPP4 in the plasma and sputa of 14 MERS-CoV-infected patients of various degrees of disease severity. The concentration of sDPP4 in the plasma of MERS patients (474.76 ± 108.06 ng/ml) was significantly lower than those of healthy controls (703.42 ± 169.96 ng/ml), but there were no significant differences among the patient groups. Interestingly, plasma levels of IL-10 and EGF were negatively and positively correlated with sDPP4 concentrations, respectively. The sDPP4 levels in sputa were less than 300 ng/ml. Viral infection was inhibited by 50% in the presence of more than 8000 ng/ml of sDPP4. Therefore, sDPP4 levels in the plasma of MERS patients are significantly reduced below the threshold needed to exert an antiviral effect against MERS-CoV infection.

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sDPP4, a soluble form of MERS-CoV receptor, in plasma is reduced in MERS patients.

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IL-10 and EGF in plasma are negatively and positively correlated with sDPP4.

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sDPP4 levels of MERS patients are not sufficient to exert an antiviral effect.

Activatable Near-Infrared Fluorescent Probe for Dipeptidyl Peptidase IV and Its Bioimaging Applications in Living Cells and Animals

Visualization of endogenous disease-associated enzymes is of great clinical significance, as it could allow earlier clinical diagnosis and timely intervention. Herein, we first synthesized and characterized an enzyme-activatable near-infrared fluorescent probe, GP-DM, for determining the activity of dipeptidyl peptidase IV (DPP IV), which is associated with various pathological processes, especially in diabetes and malignant tumors. GP-DM emitted significant turn-on NIR fluorescent signals simultaneously in response to DPP IV, making it favorable for accurately and dynamically monitoring DPP IV activity in vitro and in vivo. GP-DM exhibited excellent specificity and sensitivity in DPP IV imaging, as indicated by its higher catalytic activity than other human serine hydrolases and by its strong anti-interference ability to a complex biological matrix, which was fully characterized in a series of phenotyping reactions and inhibition assays. Encouraged by the advantages mentioned above, we successfully used GP-DM to evaluate endogenous DPP IV activity in various biological samples (plasma and tissue preparations) and living tumor cells and performed real-time in vivo bioimaging of DPP IV in zebrafish and tumor-bearing nude mice. All of the results reflected and highlighted the potential application value of GP-DM in the early detection of pathologies, individual tailoring of drug therapy, and image-guided tumor resection. Furthermore, our results revealed that DPP IV, a key target enzyme, is closely associated with the migration and proliferation of cancer cells and regulating the biological activity of DPP IV may be a useful approach for cancer therapy.

The role of renal dipeptidyl peptidase-4 in kidney disease: renal effects of dipeptidyl peptidase-4 inhibitors with a focus on linagliptin

Emerging evidence suggests that dipeptidyl peptidase-4 (DPP-4) inhibitors used to treat type 2 diabetes may have nephroprotective effects beyond the reduced renal risk conferred by glycemic control. DPP-4 is a ubiquitous protein with exopeptidase activity that exists in cell membrane-bound and soluble forms. The kidneys contain the highest levels of DPP-4, which is increased in diabetic nephropathy. DPP-4 inhibitors are a chemically heterogeneous class of drugs with important pharmacological differences. Of the globally marketed DPP-4 inhibitors, linagliptin is of particular interest for diabetic nephropathy as it is the only compound that is not predominantly excreted in the urine. Linagliptin is also the most potent DPP-4 inhibitor, has the highest affinity for this protein, and has the largest volume of distribution; these properties allow linagliptin to penetrate kidney tissue and tightly bind resident DPP-4. In animal models of kidney disease, linagliptin elicited multiple renoprotective effects, including reducing albuminuria, glomerulosclerosis, and tubulointerstitial fibrosis, independent of changes in glucagon-like peptide-1 (GLP-1) and glucose levels. At the molecular level, linagliptin prevented the pro-fibrotic endothelial-to-mesenchymal transition by disrupting the interaction between membrane-bound DPP-4 and integrin β1 that enhances signaling by transforming growth factor-β1 and vascular endothelial growth factor receptor-1. Linagliptin also increased stromal cell derived factor-1 levels, ameliorated endothelial dysfunction, and displayed unique antioxidant effects. Although the nephroprotective effects of linagliptin are yet to be translated to the clinical setting, the ongoing Cardiovascular and Renal Microvascular Outcome Study with Linagliptin in Patients with Type 2 Diabetes Mellitus (CARMELINA®) study will definitively assess the renal effects of this DPP-4 inhibitor. CARMELINA® is the only clinical trial of a DPP-4 inhibitor powered to evaluate kidney outcomes.

DPPIV promotes endometrial carcinoma cell proliferation, invasion and tumorigenesis

Dipeptidyl peptidase IV (DPPIV), also known as CD26, is a 110-kDa cell surface glycoprotein expressed in various tissues. DPPIV reportedly plays a direct role in the progression of several human malignancies. DPPIV specific inhibitors are employed as antidiabetics and could potentially be repurposed to enhance anti-tumor immunotherapies. In the present study, we investigated the correlation between DPPIV expression and tumor progression in endometrial carcinoma (EC). DPPIV overexpression altered cell morphology and stimulated cell proliferation, invasion and tumorigenesis in vitro and in vivo. These effects were abrogated by DPPIV knockdown or pharmacological inhibition using sitagliptin. DPPIV overexpression increased hypoxia-inducible factor 1a (HIF-1a) and vascular endothelial growth factor A (VEGFA) expression to promote HIF-1a-VEGFA signaling. Our results indicated that DPPIV accelerated endometrial carcinoma progression and that sitagliptin may be an effective anti-EC therapeutic.

Molecular Evidence of Adenosine Deaminase Linking Adenosine A2A Receptor and CD26 Proteins

Adenosine is an endogenous purine nucleoside that acts in all living systems as a homeostatic network regulator through many pathways, which are adenosine receptor (AR)-dependent and -independent. From a metabolic point of view, adenosine deaminase (ADA) is an essential protein in the regulation of the total intracellular and extracellular adenosine in a tissue. In addition to its cytosolic localization, ADA is also expressed as an ecto-enzyme on the surface of different cells. Dipeptidyl peptidase IV (CD26) and some ARs act as binding proteins for extracellular ADA in humans. Since CD26 and ARs interact with ADA at opposite sites, we have investigated if ADA can function as a cell-to-cell communication molecule by bridging the anchoring molecules CD26 and A2AR present on the surfaces of the interacting cells. By combining site-directed mutagenesis of ADA amino acids involved in binding to A2AR and a modification of the bioluminescence resonance energy transfer (BRET) technique that allows detection of interactions between two proteins expressed in different cell populations with low steric hindrance (NanoBRET), we show direct evidence of the specific formation of trimeric complexes CD26-ADA-A2AR involving two cells. By dynamic mass redistribution assays and ligand binding experiments, we also demonstrate that A2AR-NanoLuc fusion proteins are functional. The existence of this ternary complex is in good agreement with the hypothesis that ADA could bridge T-cells (expressing CD26) and dendritic cells (expressing A2AR). This is a new metabolic function for ecto-ADA that, being a single chain protein, it has been considered as an example of moonlighting protein, because it performs more than one functional role (as a catalyst, a costimulator, an allosteric modulator and a cell-to-cell connector) without partitioning these functions in different subunits.

Dipeptidyl peptidase inhibitor therapy in type 2 diabetes: Control of the incretin axis and regulation of postprandial glucose and lipid metabolism

Dipeptidyl peptidase 4 (DPP4) is a widely expressed, serine protease which regulates the bioactivity of many peptides through cleavage and inactivation including the incretin hormones, glucagon like peptide -1 (GLP-1) and glucose dependent insulinotropic polypeptide (GIP). Inhibitors of DPP4 are used therapeutically to treat patients with Type 2 Diabetes Mellitus (T2DM) as they potentiate incretin action to regulate islet hormone secretion and improve glycemia and post-prandial lipid excursions. The widespread clinical use of DPP4 inhibitors has increased interest in the molecular mechanisms by which these drugs mediate their beneficial effects. Traditionally, focus has remained on inhibiting the catalytic activity of DPP4 within the plasma compartment, however evidence is emerging on the importance of inactivation of membrane-bound DPP4 in selective tissue beds to potentiate local hormone gradients. Here we review the recent advances in identifying the cellular sources of both circulating and membrane-bound DPP4 important for cleavage of the incretin hormones and regulation of glucose and lipoprotein metabolism.